Back pain is one of the most common and often debilitating conditions affecting millions of people. Some forms of back pain are muscular in nature and may be simply treated by rest, posture adjustments and painkillers. For example, lower back pain (LBP) is a very common condition that may be caused by unusual exertion or injury. Unusual exertion such as heavy lifting or strenuous exercise may result in back pain due to a pulled muscle, a sprained muscle, a sprained ligament, a muscle spasm, or a combination thereof. An injury caused by falling down or a blow to the back may cause bruising. These forms of back pain are typically non-chronic and may be self-treated and cured in a few days or weeks.
Other types of non-chronic back pain may be treated by improvements in physical condition, posture and/or work conditions. Being pregnant or otherwise being significantly overweight may cause LBP. A mattress that does not provide adequate support may cause back pain in the morning. Working in an environment lacking good ergonomic design may also cause back pain. In these instances, the back pain may be cured by eliminating the underlying cause. Whether it is excess body weight, a bad mattress, or a bad office chair, these forms of back pain are readily treated.
It is estimated that over ten million people in the United States alone suffer from persistent back pain. Approximately half of those suffering from persistent back pain are afflicted with chronic disabling pain, which seriously compromises a person's quality of life and is the second most common cause of worker absenteeism. Further, the cost of treating chronic back pain is very high, even though the majority of sufferers do not receive treatment due to health risks, limited treatment options, and/or inadequate therapeutic results. Thus, chronic back pain has a significantly adverse effect on a person's quality of life, on industrial productivity, and on heath care expenditures.
Some forms of back pain are the result of disorders directly related to the spinal column, which disorders are not readily treated. While some pain-causing spinal disorders may be due to facet joint degradation or degradation of individual vertebral masses, disorders associated with the intervertebral discs are predominantly affiliated with chronic back pain (referred to as disc related pain). The exact origin of disc related pain is often uncertain, and although some episodes of disc related pain may be eased with conservative treatments such as bed-rest and physical therapy, future episodes of disc related pain are likely to occur periodically.
There are a number of suspected causes of disc related pain, and in any given patient, one or more of these causes may be present. However, the ability to accurately diagnose a specific cause or locus of pain is currently difficult. Because of this uncertainty, many of the causes of disc related pain are often lumped together and referred to as degenerative disc disease (DDD).
A commonly suspected source of disc related pain is physical impingement of the nerve roots emanating from the spinal cord. Such nerve root impingement may have a number of different underlying causes, but nerve root impingement generally results from either a disc protrusion or a narrowing of the intervertebral foramina (which surround the nerve roots).
As a person ages, their intervertebral discs become progressively dehydrated and malnourished. Due to the combination of aging and continued stressing, the discs begin to degenerate. With continued degeneration, or an excessive stressing event, or both, the annulus fibrosus of a disc may tear, forming one or more fissures (also referred to as fractures). Such fissures may progress to larger tears, which allow the gelatinous material of the nucleus pulposus to flow out of the nucleus and into the outer aspects of the annulus. The flow of the nucleus pulposus to the outer aspects of the annulus may cause a localized bulge or herniation.
When herniation of the nucleus/annulus occurs in the posterior portions of the disc, nerve roots may be directly and physically impinged by the bulge. In more extreme or progressed instances of annular tears, the nuclear material may escape, additionally causing chemical irritation of the nerve roots. Dependent upon the cause and nature of the disc protrusion, the condition may be referred to as a disc stenosis, a disc bulge, a herniated disc, a prolapsed disc, a ruptured disc, or, if the protrusion separates from the disc, a sequestered disc.
Dehydration and progressive degeneration of a disc also leads to thinning of the disc. As the thickness of the disc reduces, the intervertebral foraminae become narrow. Because the nerve roots pass through the intervertebral foraminae, such narrowing may mechanically entrap the nerve roots. This entrapment can cause direct mechanical compression or it may tether the roots, causing excessive tension to the roots during body movement.
Nerve root impingement most often occurs in the lumbar region of the spinal column since the lumbar discs bear significant vertical loads relative to discs in other regions of the spine. In addition, disc protrusions in the lumbar region typically occur posteriorly because the annulus fibrosus is radially thinner on the posterior side than on the anterior side and because normal posture places more compression on the posterior side. Posterior protrusions are particularly problematic since the nerve roots are posteriorly positioned relative to the intervertebral discs. Lower back pain due to nerve root irritation not only results in strong pain in the region of the back adjacent the disc, but may also cause sciatica, or pain radiating down one or both legs. Such pain may also be aggravated by such subtle movements as coughing, bending over, or remaining in a sitting position for an extended period of time.
Another suspected source of disc related back pain is damage and irritation to the small nerve endings which lie in close proximity to or just within the outer aspects of the annulus of the discs. Again, as the disc degenerates and is subjected to stressing events, the annulus fibrosus may be damaged and form fissures. While these fissures can lead to pain via the mechanisms described above, they may also lead to pain emanating from the small nerve endings in or near the annulus, due to mechanical or chemical irritation at the sites of the fissures. The fissures may continue to irritate the small nerve endings, as their presence causes the disc to become structurally weaker, allowing for more localized straining around the fissures. This results in more relative motion of edges of the fissures, increasing mechanical irritation. Because it is believed that these fissures have only limited healing ability once formed, such irritation may only become progressively worse.
A common treatment for a disc herniation is a discectomy, a procedure wherein the protruding portion of the degenerated disc is surgically removed. However, discectomy procedures have an inherent risk since the portion of the disc to be removed is immediately adjacent the nerve root, and any damage to the nerve root is clearly undesirable. Furthermore, discectomy procedures are not always successful long term because scar tissue may form and/or additional disc material may subsequently protrude or reherniate from the disc space as the disc deteriorates further. The recurrence of a disc herniation may necessitate a repeat discectomy procedure, along with its inherent clinical risks and less than perfect long term success rate. Thus, a discectomy procedure, at least as a stand-alone procedure, is clearly not an optimal solution.
Discectomy is also not a viable solution for DDD when no disc/nuclear herniation is involved. As mentioned above, DDD causes the entire disc to degenerate, narrowing the intervertebral space and shifting the load to the facet joints. If the facet joints carry a substantial load, the joints may degrade over time and be a different cause of back pain. Furthermore, the narrowed disc space can result in the intervertebral foramina surrounding the nerve roots directly impinging on one or more nerve roots. Such nerve impingement is very painful and cannot be corrected by a discectomy procedure. Furthermore, a discectomy does not address pain caused by annular fissures or post-surgical defects, which may cause direct mechanical irritation to the small nerve endings near or just within the outer aspect of the annulus of a damaged disc.
As a result of the limitations of a discetomy, spinal fusion, particularly with the assistance of interbody fusion cages, has become a preferred secondary procedure, and in some instances, a preferred primary procedure. Spinal fusion involves permanently fusing or fixing adjacent vertebrae. Hardware in the form of bars, plates, screws, and cages may be utilized in combination with bone graft material to fuse adjacent vertebrae. Spinal fusion may be performed as a stand-alone procedure, or it may be performed in combination with a discectomy procedure. By placement of the adjacent vertebrae in their normal position and fixing them in place, relative movement therebetween may be significantly reduced and the disc space may be restored to its normal condition. Thus, theoretically, aggravation caused by relative movement between adjacent vertebrae may be reduced if not eliminated.
The success rate of spinal fusion procedures is certainly less than perfect for a number of different reasons, none of which are well understood. In addition, even if spinal fusion procedures are initially successful, they may cause accelerated degeneration of adjacent discs since the adjacent discs must accommodate a greater degree of motion. The degeneration of adjacent discs simply leads to the same problem at a different anatomical location, which is clearly not an optimal solution. Furthermore, spinal fusion procedures are invasive to the disc, risk nerve damage, and, dependent upon the procedural approach, are technically complicated (endoscopic anterior approach), invasive to the bowel (surgical anterior approach), and/or invasive to the musculature of the back (surgical posterior approach).
Another procedure that has been less than clinically successful is total disc replacement with a prosthetic disc. This procedure is also very invasive to the disc, and, dependent upon the procedural approach, either invasive to the bowel (surgical anterior approach) or invasive to the musculature of the back (surgical posterior approach). In addition, the procedure may actually complicate matters by creating instability in the spine, and the long-term mechanical reliability of prosthetic discs has yet to be demonstrated.
Many other medical procedures have been proposed to solve the problems associated with degenerative discs or disc protrusions. However, many of the proposed procedures have not been clinically proven, and some of the allegedly beneficial procedures have controversial clinical data. There is a substantial need for improvements in the treatment of spinal disorders, particularly in the treatment of disc related pain associated with a damaged or otherwise unhealthy disc, specifically the repair of disc defects or annulo-nucleoplasty regeneration.